I was teaching my young nephew some math the other day, and from discussing the typical sort of word problems he's encountering in class, I noticed that the "-th" suffix adds a distinct meaning to adjectives. For example:
- If a ship is long, it has length.
- If a woman is wide, she has width.
- If a person is strong, he possesses strength.
- If what I say is true, I'm speaking truth.
- A lumbering panda moving slow is full of sloth.
Now, I've learned some linguistics from English L&U, and I'm guessing this "-th" suffix is an affix that changes adjectives into nouns. My questions are: What exactly is this "-th" suffix adding to the meaning? Secondly, does the "-th" originate from a separate word in Old English? Lastly, is there something to say about the vowel shifts that seems to be occurring in some of the transformations (e.g., strong going to strength) that somehow fits in with the ablaut system of strong verbs/weak verbs, that I learned of from the excellent responses to my previous question?
Best Answer
It is, as you say, a nominalising suffix, that goes back at least to Common Germanic. It usually surfaces as "-th" in English, but as "-t" after a (historical) "-(g)h": "height", "weight", "sight", "flight".
The vowel alternations are mostly a matter of length (though I admit that the "-ong"/"-ength" alternation sounds a bit like IE ablaut). "Wide" in Old and Middle English was bisyllabic, with a long vowel, whereas "widþ" had one closed syllable and therefore a short vowel. Only the long vowel went waltzing round the mouth in the Great Vowel Shift. Thinking about it, this particular alternation may go back to a time when the IE ablaut was operating, but I'm not sure.